I can understand that this migh
https://www.classiccarstereo.co.uk/...o-speakers/7-x-5-dual-voice-coil-loudspeaker/
I fitted this dual voice speaker under the dash. It replaced the old factory speaker. This adds to the door speakers which weren’t enough on their own.
t not be loud enough for rear seat passengers, but in my family's Westfalia Continental, the Javelin mono radio (VHF plus long, medium & short wave) with single speaker in the dashboard top, was loud enough in for front-cab seat occupants.
Japanese made, Javelin 9044, single-speaker, mono radio (serial No. 2090540), with Long Wave: 150~280 kHz; Medium Wave: 540~1600 kHz; Short Wave: 5·95~6·2 MHz; VHF (aka FM): 88~108 MHz, which was originally retro-fitted in 1975, to my family's British specification, 1973 VW 1600 Type 2, Westfalia Continental campervan.
The radio also featured a 6-pin DIN socket for a tape player or recorder connection, the option of 4 ohm or 8 ohm speaker impedance and push-button pre-settable radio stations
I have since chosen to replace it, with a mid 1980s vintage, Blaupunkt Toronto SQR46, four-speaker, stereo radio & audio-cassette player, which also features SHORT, medium & long wave bands, plus FM (aka VHF).